R. C. VON BORSTEL 177 



The females of Habrobracon are diploid and the males are hap- 

 loid — unfertilized eggs become haploid males, females originate 

 from fertilized eggs. When eggs are fertilized by sperm contain- 

 ing the same sex alleles as the egg pronuclei, diploid males result 

 (P. W. Whiting, 1943b). This sex determination mechanism 

 appears to occur also in the honey bee, Apis mellifera L. ( Mack- 

 ensen, 1951, 1955). 



The morphology of meiosis and early embryogeny of Habro- 

 bracon has been studied in detail by Torvik-Greb ( 1935 ) , Hen- 

 schen ( 1928 ) , and Speicher ( 1936 ) . The description given in this 

 review is, for the most part, summarized from the analysis of 

 Speicher. Oogenesis in most insects differs from this form only in 

 details (Wilson, 1928; Sonnenblick, 1950); the description here 

 is restricted to Habrobracon. The female has four ovarioles, each 

 with a uterine sac where mature eggs are stored prior to oviposi- 

 tion (Fig. 1).* One ovariole with attached uterine sac is shown 

 in Fig. 2. The egg arises from a nest of 32 oogonia, 31 of which 

 become nurse cells. (Henschen, 1928, reported a nest of 16 

 oogonia, but as is apparent from the number of heavily staining 

 nuclei in Fig. 3, more than 15 nurse cells normally exist.) Dur- 

 ing oocyte growth the nurse cells gi^ow too. While the oocyte 

 becomes larger the oocyte nucleus proceeds through the long first 

 meiotic prophase, and the nurse cell nuclei go through several 

 cycles of polysomatic enlargement; the nuclei in nurse cells next 

 to the oocyte are somewhat larger than the nurse cell nuclei 

 farthest from the oocyte. Just prior to entrance of the egg into 

 the uterine sac from the ovariole, the nuclei of the nurse cells 

 disintegrate and are injected into or are engulfed by the egg 

 (Fig. 4). It has been suggested (Painter, 1940; Zeuthen, 1951) 

 that this broken down deoxyribonucleic acid is incorporated into 

 nuclei during the ensuing rapid mitoses. The point might be 

 raised that some of the genetic structure could be passed intact 

 from the deoxyribonucleic acid of the mother to the nuclei of 

 the embryo. This would be equivalent to transformation ( Hotch- 

 kiss, 1955) and has not been observed. Most of the deoxyribo- 



** The photomicrographs (Figs. 1-4) were made by Henry H. Jones, of 

 the Carnegie Institution of Washington, Cold Spring Harbor, N. Y. 



